Sunday, June 9, 2013

Rubies! Did you know...??

I love rubies!  Well, who doesn't?  They're so beautiful and the distinctive pink-red color of the stone can be seen from far away, so ruby jewelry is always noticed!

Queen Elizabeth's Burmese Ruby Tiara
A ruby is a "red sapphire".  Sapphires come in every color of the rainbow, but when it's red it's called a ruby!

Rubies are almost always heat treated to enhance the color and vibrancy.  In the jewelry industry, heat treatment is assumed (unless otherwise specified).   The Gemological Institute of America (GIA) accepts this treatment, as it is permanent and will never degrade over time.  It's like a continuation of the natural heating of the stone!  A ruby is heated to improve its clarity and color. At temperatures above 1700 degrees Celsius, the "silk" (rutile needles in the stone) dissolves and improves the color and clarity of the stone.   Jewelers can determine if a ruby has been heat treated by the lack of "silk" in the stone.

And there are other treatments available:
  • Fracture filling (with glass!) to fill in cavities or fractures in the stone (see below);
  • Surface diffusion (applying a coating on the stone to enhance color);
  • Dying the stone
  • Oiling the stone
  • Waxing the stone
Dying, oiling and waxing are not permanent and may require future treatment!

Sellers of treated rubies (whether loose stones or set in jewelry)  should ALWAYS tell the consumer about the treatments/enhancements done to the ruby.  Hiding this information is dishonest, to say the least.

Untreated, natural rubies are VERY rare and very expensive---they can demand prices at over $20,000 a carat!  

Lead Glass Filling:

Glass Fracture-Filled Ruby - $36.72, 1.36 ct
Filling the fractures inside the ruby with lead glass (or a similar material) dramatically improves the transparency of the stone.  This is done in four steps:
  1. The rough stones are pre-polished;
  2. The rough is cleaned with hydrogen fluoride;  
  3. The first heating process during which no fillers are added. The heating process eradicates impurities inside the fractures.
  4. The second heating process in an electrical oven with different chemical additives, including lead glass powder.  The ruby is dipped into oils, then covered with powder, embedded on a tile and placed in the oven where it is heated at around 900 °C (1600 °F) for one hour in an oxidizing atmosphere. The orange colored powder transforms upon heating into a transparent to yellow-colored paste, which fills all fractures. After cooling the color of the paste is fully transparent and dramatically improves the overall transparancy of the ruby.  This process can be repeated three or four times using different additives.
If a color needs to be added, the glass powder can be "enhanced" with copper or other metal oxides as well as elements such as sodium, calcium, potassium etc.

The treatment can easily be determined using a 10x loupe to see bubbles either in the cavities or in the fractures that were filled with glass.

Heated Treated Ruby - 2.1 Carats, $2,

A reputable seller will ALWAYS tell a customer if the ruby has been heat treated, fracture-filled, or been given another treatment.

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